U.S. patent number 7,052,527 [Application Number 10/834,215] was granted by the patent office on 2006-05-30 for thermal spray composition and method of deposition for abradable seals.
This patent grant is currently assigned to Sulzer Metco (Canada) Inc.. Invention is credited to Petr Fiala, Karel Hajmrle.
United States Patent |
7,052,527 |
Hajmrle , et al. |
May 30, 2006 |
Thermal spray composition and method of deposition for abradable
seals
Abstract
A thermal spray composition and method of deposition for
abradable seals for use in gas turbine engines, turbochargers and
steam turbines. The thermal spray composition comprises a mixture
of metal-clad solid lubricant particles and unclad solid lubricants
particles for producing an abradable seal used in the compressor
section of gas engines, aircraft engines, radial compressors and
the like. The metal is selected from alloys of Ni, Co, Cu, Fe and
Al, preferably Ni alloys, and the solid lubricant is at least one
of hexagonal boron nitride, graphite, calcium fluoride, lithium
fluoride and molybdenum disulphide, preferably hexagonal boron
nitride or hexagonal boron nitride and graphite.
Inventors: |
Hajmrle; Karel (Edmonton,
CA), Fiala; Petr (Edmonton, CA) |
Assignee: |
Sulzer Metco (Canada) Inc.
(Fort Sasketchewan, CA)
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Appl.
No.: |
10/834,215 |
Filed: |
April 29, 2004 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20050287390 A1 |
Dec 29, 2005 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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10346124 |
Jan 17, 2003 |
6808756 |
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Field of
Search: |
;75/252 ;106/286.1
;428/402,457,564,688 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Mai; Ngoclan T.
Attorney, Agent or Firm: Fors; Arne I.
Parent Case Text
This application is a Divisional of application Ser. No. 10/346,124
filed Jan. 17, 2003 now U.S. Pat. No. 6,808,756.
Claims
The invention claimed is:
1. A thermal spray powder composition for an abradable seal
comprising about 70 to 95 wt % of a metal-clad solid lubricant and
about 5 to 30 wt % solid lubricant.
2. A thermal spray powder composition for an abradable seal
comprising about 80 to 90 wt % of a metal-clad solid lubricant and
about 10 to 20 wt % of unclad solid lubricant.
3. A thermal spray composition as claimed in claim 1, in which the
solid lubricant is at least one lubricant powder selected from the
group consisting of hexagonal boron nitride, graphite, calcium
fluoride, lithium fluoride, magnesium fluoride, barium fluoride,
tungsten disulfide and molybdenum disulfide particles.
4. A thermal spray composition as claimed in claim 1, in which the
solid lubricant is a mixture of hexagonal boron nitride and
graphite particles.
5. A thermal spray composition as claimed in claim 1, in which the
solid lubricant is hexagonal boron nitride particles.
6. A thermal spray composition as claimed in claim 3, in which the
thermal spray composition is a powder, a wire or a rod and in which
the metal alloy cladding is selected from the group consisting of
Ni, Co, Cu, Fe, Al, and combinations and alloys thereof.
7. A thermal spray composition as claimed in claim 4, in which the
metal alloy cladding is selected from the group consisting of Ni,
Co, Fe and combinations and alloys thereof.
8. A thermal spray composition as claimed in claim 5, in which the
metal alloy cladding is Ni, NiCr, NiCrAl or Ni alloy.
9. A thermal spray composition as claimed in claim 5, in which the
metal alloy cladding is NiCrAl.
10. A thermal spray composition as claimed in claim 5, in which the
metal alloy cladding is selected from the group consisting of Ni,
Co, Fe and combinations and alloys thereof.
11. An abradable seal for gas turbine engines, turbo changers,
compressors or steam turbines produced by applying an adherent
coating having a thickness up to 3 mm to a substrate by thermally
spraying a composition thereon comprising about 70 to 95 wt % of a
metal-clad solid lubricant comprised of hexagonal boron nitride
clad with a metal selected from the group consisting of Ni, NiCr,
NiCrAl and Ni alloy, and about 5 to 30 wt % of a solid lubricant
comprised of hexagonal boron nitride.
Description
BACKGROUND OF THE INVENTION
(i) Field of the Invention
This invention relates to abradable seals and, more particularly,
relates to high-temperature abradable seal compositions for use in
gas turbine engines, turbochargers, compressors, steam turbines and
the like.
(ii) Description of the Related Art
Basic requirements for abradable seals in the compressor section of
gas turbine engines include good abradability, spall resistance,
and erosion resistance. Abradable seals are also required to
exhibit low gas permeability, a smooth surface, good aging
properties and long-term oxidation resistance at high temperatures.
In the case of abradability, the seal is a sacrificial element, it
being desirable to minimize blade wear. Additionally, low gas
permeability is required in order to minimize gas flow through the
seal itself. It has been shown that low permeable seals with a
smooth surface finish improve overall compressor efficiency by
about one percent as compared to conventional permeable seals. In
addition, low permeability of the seal prevents entrapment of fine
particles, e.g. dust or grit, which can act as an abrasive against
the blade tips, thus wearing them unevenly. Smooth surface finishes
in the gas path improve overall airflow, also contributing to
efficiency. Finally, long-term oxidation resistance is required due
to increases in compressor operating temperature up to 815.degree.
C.
There are several air seals used in a compressor section of a gas
or aircraft engine. Historically the oldest is feltmetal that
comprises a plurality of metal fibres. The feltmetal is described
for example in U.S. Pat. No. 4,257,735. The most important
disadvantages of this seal are that it has to be brazed to the
substrate material and that it is highly porous.
Typical jet engine compressor air seals include a metal matrix of
aluminum-silicon with embedded polymer particles or hexagonal boron
nitride powder particles as described in U.S. Pat. No. 3,723,165
and U.S. Pat. No. 5,506,055, respectively. The disadvantage of
these systems is their limited temperature capability at
315.degree. C. for the system with polymer and 480.degree. C. for
the system with hexagonal boron nitride. In the former case, the
temperature capability is governed by the polymer and in the latter
case it is governed by the aluminum silicon alloy.
Abradable materials used at high temperatures in the compressor
section of turbine engines are usually NiCrAl/Bentonite coatings
described in U.S. Pat. Nos. 4,374,173 and 4,291,089 by Adamovic.
However, NiCrAl/Bentonite seals do not rub well against Ti alloy
blades. These coatings perform well against Ni alloy and steel
blades but, when Ti alloy blades are used, the blade tips overheat
and are subject to wear. Sometimes, glazing of the coating is
observed.
Another known abradable seal is that prepared by the techniques of
Rangaswamy et al., described in U.S. Pat. No. 5,434,210. A
composite powder for thermal spraying of abradable coatings is
disclosed in which the composite powder contains three components.
One component is any of a number of metal or ceramic matrix
materials, another component is a solid lubricant, and the third
component is a polymer. Typical as-sprayed coatings comprise a Co
alloy matrix with dispersed particles of hexagonal boron nitride
and polymer. The polymer is subsequently burned out and the final
very porous structure contains only hexagonal boron nitride
particles dispersed throughout the Co-based matrix. The coatings
prepared from this material have acceptable abradability but low
erosion resistance. The erosion resistance is required in order to
maintain uniform clearances throughout the life of the engine or
engine performance characteristics are adversely affected.
Conventional commercial turbine engines have exhibited a two
percent increase in airflow around blade tips as a result of seal
erosion after approximately 3,000 flights. Much of this may be
attributed to erosion of the abradable seal and blade airfoil tip,
and to rub interactions between the blade tips and the seal. In
military engine applications, where gas path velocities are
relatively high, erosion resistance is of paramount importance.
Moreover, high permeability due to open porosity of conventional
seals enables back leakage of gas, which decreases engine
efficiency.
We have found that the use of Ni alloy-clad hexagonal boron nitride
powder applied by flame or plasma spraying provided an abradable
seal which exhibited poor combination of erosion resistance and
abradability. When erosion resistance was acceptable, the
abradability was poor. When abradability was satisfactory, the
erosion resistance was poor. Ni alloy-clad boron nitride,
accordingly, is not suitable for use as an abradable seal.
It is accordingly a principal object of the present invention to
provide a novel thermal spray composition and its method of
application for producing an abradable seal.
A further object of the invention is the provision of an abradable
seal, for use in gas turbine engines having good abradability,
spall resistance and erosion resistance, particularly when used in
conjunction with titanium-alloy blades.
It is another object of the present invention to provide an
abradable seal having a smooth surface, low permeability, good
thermal conductivity, low interparticle cohesive strength and
long-term oxidation and glazing resistance resulting in favourable
long-term aging characteristics.
SUMMARY OF THE INVENTION
In its broad aspect, the thermal spray powder composition of the
invention for an abradable seal comprises a mixture of metal clad
lubricant powder and unclad lubricant powder, said mixture having
about 5 to 30 wt %, preferably about 10 to 20 wt %, unclad
lubricant powder, and about 70 to 95 wt %, preferably about 80 to
90 wt %, of a metal-clad solid lubricant powder having a size in
the range of 10 to 150 microns. The composition can be in the form
of a powder or a powder consolidated as a wire or rod. The solid
lubricant is at least one of hexagonal boron nitride, graphite,
calcium fluoride, lithium fluoride and molybdenum disulphide
particles, preferably hexagonal boron nitride powder or a mixture
of hexagonal boron nitride and graphite. The matrix-forming metal,
a metal alloy cladding, is selected from Ni, Co, Cu, Fe, Al, and
combinations and alloys thereof, particularly nickel alloys such as
NiCrAl and NiCr, and CuAl and AlSi.
The matrix-forming metal alloy and the solid lubricant can also
contain some other elements as impurities, that significantly do
not alter the seal properties.
The composition can also contain a fugitive phase to create
porosity after the elimination from the abradable coating, the
fugitive phase consisting at least one of salt, sugar and other
fugitive materials.
In accordance with another broad aspect of the invention, the
composition comprises about 70 to 95 wt % of a metal alloy-clad
solid lubricant and about 5 to 30 wt % of unclad solid
lubricant.
The method of providing an abradable seal on a substrate comprises
applying an adherent coating of the said powder composition having
a thickness of up to 3 mm to the substrate by thermally spraying
the powder composition thereon such as by plasma spraying,
combustion spraying or wire spraying.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The abradable seal of the present invention comprises a
matrix-forming metal or metal alloy component and a solid lubricant
component, wherein the two components provide a synergism in
abradable coatings which have unexpected superior characteristics
over prior art materials. The matrix-forming metal alloy present as
a metal cladding on a solid lubricant powder is selected from the
metals Ni, Co, Cu, Fe, Al and combinations and alloys thereof,
preferably NiCrAl, NiCr, CuAl and AlSi. The solid lubricant is
typified by lubricants such as hexagonal boron nitride, graphite,
calcium fluoride, lithium fluoride and molybdenum disulphide
particles, preferably hexagonal boron nitride or hexagonal boron
nitride and graphite particles. A preferred composition of metal
alloy clad on a solid lubricant is hexagonal boron nitride or
hexagonal boron nitride and graphite particles clad with NiCrAl
alloy. The metal-clad solid lubricant particles are blended with
unclad particles of solid lubricant particles such as hexagonal
boron nitride or hexagonal boron nitride and graphite available
from commercial suppliers.
The unclad solid lubricant component comprises at least 5 wt % and
not more than 30 wt % of the composition, preferably 10 to 20 wt %
of the composition, the balance comprising the metal clad solid
lubricant component. The metal-clad solid lubricant component
comprises at least 60 wt % and not more than 95 wt % of a metal
phase and at least 5 wt % and not more than 40 wt % of a solid
lubricant phase.
Although the description proceeds herein with reference to a blend
of metal-clad solid lubricant particles and unclad solid lubricant
particles, it will be understood that the powder composition may
also be prepared in the form of agglomerated particles or in the
form of wire or rod.
The two-phase powder composition of the invention preferably is
applied to a substrate by thermal spray to form an abradable seal.
Thermal spraying involves the softening or melting of a heat
fusible metal component material by heat and propelling the
softened or melted material in particulate form against a surface
to be coated. The heated particles strike the surface where they
are cooled and bonded thereto. The solid lubricant particles impact
the coating surface and adhere to it mainly by mechanical
interlocking. Usually the percentage of solid lubricant in the
coating is less than in the powder because the metal-clad particle
sticks better to the target than the solid lubricant particle. A
conventional thermal spray gun may be used for the purpose of the
both heating and propelling the particles.
A thermal spray gun normally utilizes a combustion or plasma or
electric arc to produce the heat for melting of the powder
particles. In a powder type combustion thermal spray gun, the
carrier gas, which entrains and transports the powder, is typically
an inert gas such as argon. In a plasma spray gun, the primary
plasma gas is generally argon or nitrogen. Hydrogen or helium is
usually added to the primary plasma gas, and the carrier gas is
generally the same as the primary plasma gas. Other thermal spray
methods could also be used. A good general description of thermal
spraying is provided in U.S. Pat. No. 5,049,450.
The matrix-forming metal-clad solid lubricant powder such as
NiCrAl-clad hexagonal boron nitride can be dry blended and mixed
with the unclad powder such as hexagonal boron nitride. The matrix
metal alloy holds the particles of the solid lubricant in place and
adherently bonds the coating to the substrate.
The solid lubricant particles are uniformly dispersed throughout
the deposited coating. Thus any material removal that occurs does
not change coating properties of the remaining seal. Coatings of
the invention prepared by thermal spraying the coating composition
onto a substrate have an excellent combination of abradability and
erosion resistance as a result of the coating properties including
low coating cohesive strength, low porosity, low surface roughness
and high thermal conductivity. As a result, the coatings can be
effectively used in combination with titanium-alloy blades without
danger of titanium fire, coating glazing or excessive blade wear.
Overall engine efficiency is increased.
The powder composition is typically prepared as a blend. The
metallic content of the metal-clad solid lubricant component
provides coating matrix that holds the solid lubricant particles in
place, bonds the coating to the substrate and provides oxidation
resistance. An addition of the unclad solid lubricant powder
component causes a decrease in the hardness and strength of the
metallic matrix material owing to separation of metallic particles
by solid lubricant particles and enhances the ejection of the
particles from the coating when abraded. Due to its softness it
decreases blade wear and improves abradability. The clad solid
lubricant also contributes to the decrease in the matrix strength
and hence improves abradability. During the rubbing process by
engine blades, the material abrades readily due to low matrix
strength caused by the effect of the solid lubricant particles. The
metal alloy matrix would collapse and compress during a rubbing
process without the solid lubricant filler and the coating would
become very hard with subsequent significantly decreased
abradability. Coating glazing is limited by easy particle ejection
when rubbed by a compressor blade. Coatings prepared by thermal
spraying this powder have excellent abradability and negligible
blade wear under a variety of rubbing conditions. These properties
directly follow from low coating cohesive strength, low porosity,
low surface roughness and high thermal conductivity. As a result
the coatings could be used against Ti alloy blades without danger
of Ti fire, coating glazing and excessive blade wear throughout the
full range of temperatures at which titanium blades are used (up to
600.degree. C.) and above where nickel and steel based blades are
used.
The present invention provides a number of important advantages.
The addition of unclad solid lubricant increases abradability and
decreases blade wear, without sacrificing erosion resistance.
Glazing due to severe blade rubbing is minimized, which can be
attributed to the low coating interparticle strength and good
thermal conductivity. It has been found that the enhanced thermal
conductivity due to the dense structure promotes dissipation of
heat generated during severe rub conditions, thereby decreasing the
chance of titanium fire.
It will be understood, of course, that modifications can be made in
the embodiments of the invention illustrated and described herein
without departing from the scope and purview of the invention as
defined by the appended claims.
* * * * *